This invention relates to propulsion arrangements for surface ships.
Conventional propulsion arrangements for surface ships are generally internally powered, shaft driven propeller type systems in which a drive shaft extends through the ship's hull from an internal power source to a propeller at the rear of the vessel. In order to accommodate a large diameter propeller which must be spaced from the keel of the ship and to facilitate the layout of the ship's propulsion plan equipment in the typical hull geometry, the drive propeller normally passes through the ship's hull at a downward angle so that the propeller is inclined from a vertical plane. This angled shaft arrangement reduces propeller efficiency and often causes a propeller to protrude far beyond the keel of the ship, making it susceptible to blade hits. Maintenance required by bent or broken propeller blading or shafting requires dry dock work and is expensive. In addition, severe blade impacts can also cause shaft and drive train damage, requiring hull cuts or extensive engine room disassembly for repair and may even result in flooding or lack of propulsion or maneuverability of the vessel which could result in loss of the vessel at sea. Strut-mounted pods containing individual externally driven propulsion units and pump jets have been provided to address some of the above shortcomings. Those arrangements, however, do not address all of the shortcomings of conventional propulsion arrangements nor do they offer any potential for improving overall efficiency and reducing wakes in inland or near shore waterways.
The patent to Strumskis No. 3,155,065 discloses an arrangement for propelling a ship by internally contained electric motors installed in ducts which extend through the ship's hull. Water is guided through the duct from inlets at the bow and along the sides of the ship and is driven out openings in the stern of the ship by propellers mounted within the ducts. The patent to Salo No. 4,863,404 shows a jet propulsion system for surface ships which has intake ports at the bow to receive water and outlet ports along the side and bottom and internally mounted impellers provide the motor force to the stream of water passing through internal ducts in the ship.
The Kobayashi Patent No. 5,203,728 shows a water jet propulsion unit for a water craft in which a pair of jet units is mounted at the stern of the craft in a specially formed tunnel which keeps the units separate from the overall boat structure to facilitate removal for service and repair. The hull also has access openings adjacent to jet propulsion units to permit serving without removal of the units. The impellers in the jet propulsion units are driven by shafts extending through a vertically extending wall at the forward end of the tunnel from an engine mounted within the hull of the craft. The Kobayashi Patent No. 5,462,560 and the Veronesi et al. Patent No. 5,490,768 disclose water jet propulsion units which are mounted in a hull structure so as to draw water through the hull for jet propulsion of the vessel.